The Effect of an Inert Solid Reservoir on Molecular Abundances in Dense Interstellar Clouds

TL;DR

This study uses time-dependent chemical modeling to explore how an inert solid reservoir affects molecular abundances in dense interstellar clouds, highlighting the significant impact of accretion and desorption processes.

Contribution

It provides a theoretical analysis of gas-grain interactions without surface reactions, revealing their long-term influence on molecular abundances in prestellar cores.

Findings

Gas-grain interactions cause significant long-term abundance changes.

Purely physical processes prevent chemical equilibrium during core lifetimes.

Accretion and desorption have major effects on gas-phase chemistry.

Abstract

The question, what is the role of freeze-out of chemical species in determining the molecular abundances in the interstellar gas is a matter of debate. We investigate a theoretical case of a dense interstellar molecular cloud core by time-dependent modelling of chemical kinetics, where grain surface reactions deliberately are not included. That means, the gas-phase and solid-phase abundances are influenced by gas reactions, accretion on grains, and desorption, only. We compare the results to a reference model, where no accretion occurs and only gas-phase reactions are included. We can trace that the purely physical processes of molecule accretion and desorption have major chemical consequences on the gas-phase chemistry. The main effect of introduction of the gas-grain interaction is long-term molecule abundance changes that come nowhere near an equilibrium in during the typical lifetime of a prestellar core.